An Internet Exchange Point (IXP) permits various Internet Service Providers (ISPs) to exchange traffic at designated peering points. Numbering in the hundreds on the Internet today, IXPs are a key component of the physical infrastructure of the Internet.
A network 100, shown in FIG. 1, illustrates the peering of ASes in a network without an IXP. The network includes five ASes linked by connections such as connection 110 linking AS1 and AS2. The two ASes may interconnect using a dedicated circuit and may have a business arrangement regarding costs. A connection 110 may alternatively depend on an upstream provider and may traverse long physical distances between the ASes, even if the connected ASes are geographically close.
A network 200, shown in FIG. 2, includes an exemplary IXP in the form of a layer-2 switch 205 and associated interfaces with seven ASes. One or more of the ASes may be content providers. The IXP provides peering among subscribing ASes. The arrow 210 represents a peering relationship between AS1 and AS6. Similarly, peering relationship 220 is between AS5 and AS7, and peering relationship 230 is between AS2 and AS4. An IXP keeps traffic local avoiding routing through long distance routes. The peering relationship may provide advantages to the participating subscribers in cost, latency, and bandwidth.
In the real Internet, thousands of ASes peer at several hundred IXPs and exchange a significant amount of traffic. One source estimates that IXPs carry in excess of 10TB of data per day. The peerings serve as a redundancy mechanism for ISPs while reducing dependency on upstream Tier 1 providers. Based on the amount of traffic exchanged in each direction, the costs can be distributed between the exchange points.
Members at an IXP can exchange traffic with all others connected to it, similar to hub airports where different airlines exchange passengers. Subscribers to a particular IXP, however, do not all necessarily peer with each other. For example, in the network 200, AS1 and AS5 do not have a peering relationship. A list of subscribers to a particular IXP therefore does not reveal which ASes have peering relationships.
Although IXPs carry a significant portion of Internet traffic today, little is known about them. IXPs are not visible to most topology research. The list of Internet Exchange Points (IXPs) is currently hand assembled based on contributions from individual IXPs. That list is neither complete nor accurate.
In order to obtain a list of members at an IXP, one must rely on possibly outdated voluntary information on the Internet. Previous efforts to assemble data on ASes subscribing to an IXP include efforts by the Cooperative Association for Internet Data Analysis (CAIDA) and Distributed Internet Measurements & Simulations (DIMES), which have relied on vantage points from which traditional “traceroute”-like tools are used to locate members at an IXP. Traceroute is a computer network tool used to determine the route taken by packets across an IP network.
The CAIDA approach used several dozen vantage points while the large DIMES method uses volunteers who contribute vantage points by issuing traceroute traces from many thousands of servers. In either case, the analysis of IXP member relationships has been performed by tracing packets from vantage points within the member networks. If vantage points within the members are not identified, potentially important information is missed. In spite of a large number of vantage points, existing methods do not identify vantage points for all members at all IXPs, resulting in members missing from the gathered data. Previous efforts to assemble data on IXPs are described, for example, in Y. He, G. Siganos, M. Faloutsos, S. V. Krishnamurthy, A systematic framework for unearthing the missing links: Measurements and Impact, USENIX/SIGCOMM NSDI 2007, Cambridge, Mass., USA, April 2007; K. Xu, Z. Duan, Z.-Li Zhang and J. Chandrashekar, Properties of Internet Exchange Points and Their Impact on AS Topology and Relationship, NETWORKING 2004, found at http://www.springerlink.com/content/jy3cj02rw121/?p=d5c0d5a48071465ca8b6547385e 273dc&pi=0.
There is recent anecdotal evidence of aggressive peering by certain ASes, especially large content providers. A significant portion of that peering activity takes place at the IXPs. By measuring traffic in IXPs, a researcher can get a broader idea of such shifts in traffic patterns. An IXP gives a focused view on the actual traffic traversing between ISPs at those points. There is need for an improved methodology for reverse engineering peering relationships among ASes at IXPs in the Internet to understand those relationships and to learn how IXPs evolve.